The present invention relates to a locking device, which is intended to positively hold or mount a cover or grate in a frame.
It is known to provide manholes and other ground openings with a covering, which essentially comprises a cover or grate, which is mounted in a frame. The term "frame" is not only understood to mean frame-like supports for the cover or grate, but also to define all edge or border constructions serving to mount the cover or grate. In the case of known constructions, one or more grates or covers are inserted in a frame and in general no device is provided for holding the cover in a frame. As hitherto the grates and covers have been given a relatively heavy construction, there was no particular need for holding same in the frame.
In order to save costs and materials, covers and grates have been constructionally improved and/or made from a highly loadable material, e.g. ductile cast iron in place of ordinary cast iron, which leads to a lighter structure. As such covers or grates have a higher elasticity, there is a need to provide mounts, with which the covers or grates are held in the frame.
In an earlier construction of a mount of the present applicant use has been made of a locking device insertable in the cover or grate and the parts of which cooperate with portions of the frame in such a way that with these portions and parts, is formed a positive or frictional engagement, optionally linked with a blocking possibility, so that there is a reliable mounting of the cover or grate, but whilst in part leaving a clearance. However, this earlier locking device is not able to hold the cover or grate in the frame with an initial stressing force.